Process of producing lenses.



R. STRUBEI'J.y PROCESS 0F PRODUOING LBNSES. APPLIOATION FILED 22.1. 1902.

Patented Deo. 24,'1912.

UNTT

STATES PATENT FFICE.

RUDOLF STRAUIBEL, 0F JENA, GERMANY, ASSIGNOR TO FIRM 0F CARL ZEISS, 0F JENA, GERMANY.

Specification of Letters Patent.

Patented Dec. 24, 1912.

Application flied April 1, 1909. Serial No. 487,254.

To all whom it may concern:

Be it known that I, RUDOLF Sermones, a citlzen of the German Empire, and residmo' ,at Carl-Zeiss strasse, Jena, in` the Grant surface may act as a reflecting surface. Theexpression spherical surface is intended to include the special case of a plane surface.

A proposal has alreadv appeared in the Patent Specification Nyo. Li786 (Paine, October' 3, 18116, lens perfector) of overcomingthe difficulty of manufacturing the nonsplierical surface. in the kind of lenses described, by first of all producing a lens of deviating form with .two spherical surfaces and thereupon transforming this primary lens into one of the desired form by subsi dence by heat, the mold surface being spherical and differing from the spherical lens surface to be produced only in the algebraic sign of the radius. As far as the dimensions of the primary lens are concerned, its

thicknesses at the vertex and at the margin are not at all or inappreciably different from the'respective thicknesses ofthe final lens, its two radii, however, have 'to be suitably selected. Hence in the process proposed by lfaine,` there are two elements employed as independent variables: the radii ofy the primary lens. A closer investigation of this process shows, that the selection of the rtwo, radii is insufficient to produce a lens with a spherical surface f a prescribed radius and a non-spherical surface of revolution of a prescribed profile, even though only profile curves be admitted for the latter surface, the radius of which increases or decreases steadily from the vertex to the margin. This known process is therefore in the present invention developed, so.that the calculated or otherwise given profile curve rof the surface of revolution can be realized with greater approach to accuracy than heretofore. If obtaining the spherical surface of the final lens immediately bythe mold be dispensed with, and the course be rather' to produce the final spherical surface after subsidence by grinding, the radius o the spherical mold surface offers itself as a third element which may be selected, a third independent variable. It will be noticed, that while enhancing in this way the accuracy obtainable for the non-spherical surface of the final lens, the number of the steps of the process is increased by one: the erinding of the. spherical surface of the finall lens.

Four forms of the new process can be differentiated, according as on the one hand the mold surface be concave or convex and on the other as its radius be shorter or longer than the radius of the final spherical surface. ln two of these four cases, namely, a convex mold surface of enlarged radius and a concave mold surface of diminished radius, producing the final spherical surface by grinding can only be carried out, when the thickness vat the vertex of the primary lens has been correspondingly enlarged. In the other two cases the marginal thickness of thc primary lens must be correspondingly frrenter than that of the final lens. Fihally, 1n order to obtain in the final lens the greatest approximation to the prescribed profile of the surface of revolution, the mold surface can be formed as a suitable non-spherical surface of revolution instead of according `to` a radius of a sphere to be selected. Tts profile curve is to be derived from that of the non-spherical lens surface, the dimensions of the primary lens being taken into with advantage, even when only one individual lens has to be produced.

In consequence of the perfect `adaptability of the profile of the non-spherical mold surface on the profile of the non-spheriehl lens surface to be indirectly obtained, the selection of the radii 'of the primary lens loss s/ its importance. It only serves the purp'nse of avoiding too great deviations' of 'the lens surfaceformed on the mold surface from the lin-al spherical surface. When the final lens shows no great difference between the `marginal thickness and the thickness at the vertex, a plano-parallel disk can form the primary lens. If many final lenses of this kind be intended to be produced, a mult1- plex mold with mold surfaces lying adja- -cent to each other and instead of single plano-parallel disks a planoparallel plate covering the whole mold may be employed.

The selection of thelradii of the spherical the more the practical result deviates from what resulted on paper, by so much the more therefore thev dimensions obtained graphically 'of the primary lens and of the mold surfaceI need rectification based on c Xperl ence. l

,In the cases where the primary lens rests with its margin on the edge of the mold surface, a difference in pressure between the two Iliuid media above and below the ylens canas is well known be made to assist subsidence and. thereby not only subsidence be hastened, but also the temperature employed reduced. 4

v. @In the annexed drawing:v Figure l isa section throughl a primary lens and a mold sup- ,p ort-ingit.v Fig. 2 ,is asection through the :same lens as molded by subsidence. Fig. 3 is a section'through the same lens after the final lspherical surface has been produced.

Fig. l is -the same section with the lens pro-5. files from Figs. l and 2 shown in dotted" lines. Fig. 5 isa section througha duplex primary lens l and a .mold supporting it.'

lg-G is a section through the same duplex'1 lensas molded by subsidence. Fig. 7 is a section of aliens cut o-ut from the duplex lens shown in Fig. 6 and provided ywith the final spherical surface.V Fig. S is the same section with the lens'proliles from Figs. 5` and 6 shown. in dotted lines.

In the example of the new process, to which F lgs. l to 4 are relative, the production of a collective meniscus by means of a spherical mold surface is dealt with, and in Figs. 5 to 8 dispersive mcnisci are produced with the aid of a duplex mold, the two mold t surfacesofwhich are made after the .same

non-spherical surface of revolution.

The primary lens shown in Fig. 1, being a symmetrical double convex lens, the surfaces al and 1 of which are spherical, is laid upon a mold with concave spherical mold surface c. The result of the subsidence is to bc seen from Fig. 2. A meniscus is the outcome, the upper surface Z22 of which closely approxi mates tothe prescribed non-spherical. surface of revolution, while its lower surface a2 corresponds exactly to the spherical mold surface c. rfhe lens has now to be ground, in order to replace the surface a? by the final spherical surfaced, which, as shown in Fig. 3, is weaker convex, so that the final lens d b2 with equal diameter and with the same marginal thickness zero has a Smaller vertex thickness than the primary lens al b1. In Fig. t the changes undergone by the lens are given at one view. If the primary lens had been already given the final vertex thickness and the mold surface the weaker curvature corresponding to thev final spheri- "cal surface cl, grinding would have been saved, the known process mentioned in the first paragraph above only bein applied. It is, however, easily seen from 1g. 4, that in this case a non-spherical surface of 'revof lution would. have resulted, the profile of which had diii'ered' from that of the surface b2 by a smaller vertex radiusand a.V slower reduction of the radius toward the margin of the lens.

kIn the example according to Figs. 5 to 8 two similar primary lenses each with two spherical surfaces of infinitely large radius i are contained in a glass plate with parallel plane surfaces el and f1. This plano-parallel plate is according to Fig. 5 laid upon a mold having two similar, concave, nonspherical surfaces of revolution g gv and may be held firmly in positin. at the margins by 1 a frame (shown in dotted lines).` After subsidence the plate has taken up the form represented in Fig. 6,in which it contains two lenses each with a linal non-spherical concavevsurface f2 of prescribed profile and a 110 similar convex surface c2, which is immediately produced from the concave mold surface. g.' The cutout lens in Fig. 7 presents already in place .of .the surface c2 the finalA spherical surface h yI claim: v 1.1 Process of producing alens of the two refracting surfaces of which one is a pre v scribed spherical surface and the other a produced by grinding.

non-spl1erical surface of revolution of a pro- 120 [ile approxunate'to a prescribed one, this process consisting in manufacturing a primary totally spherical lens, preparing a I.

'mold with a surface which diers from the prescribed spherical surface, placing the lens upon this mold, rendering it subsident thereupon by heat and substituting by grind lng the prescribed spherical surface ,for that lens surface which was in contact with the mold surface, the form of the said primary 13Q lens, preparing a mold tween the -mold surface and' the "prescribed spherical surface being chosen so as to cause the non-spherical surface of revolution of the final lens to approximate after subsi'- dence :is closelyas possibile tothe prescribed non-sghericalsurface ofl revolution.

2. lrocess of producing a lens of the two refine-ting surfaces oflwhich one is a prescribed spherical' surface and the other a non-spherical surface of revolution of a prescribed prole, .this process consisting in manufacturing g. primary totally spherical with a non-spherical surface of revo1ution,p1ucin'g the lens upon this mold, rendering it subsident thereupon by heat and substitutin by grinding the prescribed spherical sur ace for that nonspherical lens surface which was i Contact with the mold surface, the form o' the said primary lens and the amount of the diifei ence between the mold surface und the piehk Witnesses PAUL Knonn, Fmrz SAUBER. 

